Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Attraction and Repulsion

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Attraction and Repulsion

Attraction and repulsion have different definitions. You might have heard before that going to the beach is an attractive idea for people during the summer or how rotten food has a repulsive smell. However, in physics, we use these terms to describe the behaviour of non-contact forces. Did you know that water can be attracted to a plastic comb? Try this, grab a plastic comb and pass it through your hair several times. Now, let the faucet water run, forming a thin stream and try bringing the comb close to it.

Attraction and Repulsion Diagram showing A comb attracting a stream of water StudySmarterA comb can attract water after using passing it through your hair. StudySmarter Originals

Were you surprised? This happens because two objects can interact without touching resulting in a tendency to move closer - attraction - or to go away from each other - repulsion. We see this behaviour in charged bodies and magnets. In this article, we will explore how this works in more detail to understand when electric and magnetic forces are attractive or repulsive and how we can calculate electric force.

Meaning of attraction and repulsion in physics

As we mentioned before in physics, there is a special type of force called non-contact forces.

Non-contact forces are interactions that can affect a body's motion without the need to touch it.

Examples of non-contact forces include gravity, electrostatic, and magnetic forces.

Non-contact forces can be attractive or repulsive.

A force is attractive if the objects interacting exert a pull on each other, creating a tendency to move closer. On the other hand, a force is repulsive if the interacting objects push each other away.

Gravity is always attractive. That is why no matter where we are we feel a pull 'downwards' towards the centre of the earth. However, electrostatic and magnetic forces can be both attractive or repulsive depending on the charge of the objects involved or the pole of the magnets.

Attraction and repulsion of charges

An electrostatic force is an interaction that occurs between charged particles.

There are two types of charges: positive and negative. If two objects have the same type of charge the electrostatic force between them will be repulsive. This means that if a positively charged object gets close to another, they both will push each other away. The same occurs for two negatively charged objects.

Attraction and Repulsion Diagram of objects with the same charges feeling a repulsive force StudySmarterObjects with the same charges feel a repulsive force, StudySmarter Originals

On the other hand, opposite charges attract each other. So when one positively charged object is near a negatively charged object, they pull towards each other, tending to move closer.

Attraction and Repulsion Diagram of objects with opposite charges feeling an attractive force StudySmarterObjects with opposite charges feel an attractive force, StudySmarter Originals

Law of attraction and repulsion of electrostatic forces

In 1785, Charles-Augustin de Coulomb, measured the magnitude of electrostatic forces between charged objects using a torsion balance that he invented. He used a needle with a brass disc on one end and a counterweight on the other. The needle was suspended by a fibre so it could turn. He then charged a metallic sphere and the brass disc with the same type of charge and measured how far apart they pushed each other away by using a scale attached to the outer part of the device.

.

Attraction and Repulsion Coulomb's torsion balance StudySmarterCoulomb used a graduated torsion balance to measure the distance two charged particles push each other away, Alain Lerille CC BY-SA 3.0

After repeating this process for different amounts of charges, he was able to come up with a formula to quantify the strength of electrostatic forces. That formula is now known as Coulomb's law and it depends on the charge of the objects and the distance between them.

In this formula, the forceis measured in newtons,is the charge of the first object in coulombs, similarly,is the value of charge for second object, andis the distance between them, measured in metres. The constantis called coulomb's law constant and it depends on the medium that the charged objects are in. For example, if the objects are in a vacuum the value ofis approximately.

Attraction and repulsion between magnets

A magnet is any object or material that produces a magnetic field.

Regardless of its shape, every magnet has two poles called north (N) and south (S) poles. Similarly to the case of electric charges, unlike magnetic poles attract.

Attraction and Repulsion Diagram showing opposite poles of two magnets feeling an attractive force StudySmarterOpposite poles of two magnets feel an attractive force, StudySmarter Originals

Furthermore, same magnetic poles repel each other.

Attraction and Repulsion Illistration showing same poles of two magnets feeling a repulsive force StudySmarterSame poles of two magnets feel a repulsive force, StudySmarter Originals

The earth is like a giant magnet itself, but its geographic north pole is really a magnetic south pole. Similarly, the geographic south pole is a magnetic north pole. Because of this, a free-to-move magnet - the needle of a compass, for instance - will always align its magnetic north pole to the earth's geographical north pole, and the magnet's south pole aligns with the earth's geographic south pole. This is why magnets' poles are named that way.

Magnets work due to magnetic forces that occur in atoms forming magnetic zones in the material that act like tiny magnets themselves. Usually, these zones are randomly aligned. However, there is a special type of material called ferromagnetic. They have the property that their magnetic zones align easily when exposed to an external magnetic field, and they maintain this alignment after the magnetic field is gone, becoming magnets themselves! An object that generates a magnetic field due to its internal structure is called a permanent magnet.

Ferromagnetic materials are strongly attracted to magnets. Some examples are iron, cobalt, and nickel.

Examples of attraction and repulsion

Now that we understand how electrostatic and magnetic forces work, we will explore some daily examples where we can observe attractive and repulsive forces in action.

Examples of attraction and repulsion: Electrostatic forces

A great and very common example involves static electricity. A balloon can be negatively charged by rubbing it against your hair. When rubbing, lots of electrons 'jump' from the hair to the balloon. This results in the hair being positively charged due to the lack of electrons, and since the balloon gained those electrons, it is now negatively charged.

Attraction and Repulsion An illustration showing a ballon getting negative charge when rubbed against hair StudySmarterA balloon can be negatively charged by rubbing it against your hair, StudySmarter Originals

Now, the balloon is attracted to the positively charged hair. The electric force can be seen at a distance when the balloon is moved closer to the hair - the hair is pulled towards the balloon's surface. Both the hair and the balloon are attracted to each other.

Attraction and Repulsion An illustration showing a balloon attracting the positively charged hair StudySmarterThe balloon attracts the positively charged hair, StudySmarter Originals

Similarly, if two balloons are rubbed against some hair, both of them get negatively charged. If they are put near each other, they push each other away.

Attraction and Repulsion An illustration showing two negatively charged balloons repelling each other StudySmarterTwo negatively charged balloons repelling each other, StudySmarter Originals

As you might have deduced, this is the same reason why the comb attracts the stream of water after you pass it through your hair, it obtains an electrostatic charge!

Examples of attraction and repulsion: Magnetics forces

As we explained before, you can see attraction and repulsion due to magnetic forces when playing with two magnets. However, if you just have one magnet, you can still see how this will attract some metals. In particular, iron, cobalt, and nickel are strongly attracted to magnets since they are ferromagnetic.

Attraction and Repulsion An illustration showing a magnet attracting small pieces of metal StudySmarterA magnet attracts small pieces of ferromagnetic metal, StudySmarter Originals

A magnetic field can be generated by a current flowing through a conductor. This will make the conductor behave like a magnet. By looping a wire over a metal core and connecting it to a battery we create an electromagnet. The end connected to the positive terminal of the battery will act like the south pole of the magnet, and the end connected to the negative terminal will behave like the north pole.

Attraction and Repulsion Diagram showing a battery connected to a screw StudySmarterA current flowing through a wire can turn it into an electromagnet, StudySmarter Originals

Attraction and Repulsion - Key takeaways

  • Attraction and repulsion are characteristics of non-contact forces such as electrostatic and magnetic forces.
  • Non-contact forces are interactions that can affect a body's motion without the need to touch it. Examples of non-contact forces include electric and magnetic forces.
  • Objects having opposite charges experience an attractive electrostatic force, pulling them towards each other.
  • Objects having the same charge experience a repulsive electrostatic force, pushing them away from each other.
  • Like poles of two magnets experience an attractive magnetic force, pulling them towards each other.
  • Opposite poles of two magnets experience a repulsive magnetic force, pushing them away from each other.
  • Coulomb's law states that the force exerted between two charged objects, whether a force of attraction or repulsion, can be determined by the charge of both objects, the distance between them, and the medium in which the charges are.

Frequently Asked Questions about Attraction and Repulsion

Attraction and repulsion are characteristic of non-contact forces experienced by two objects when they are moved towards or away from each other. For example, electric and magnetic forces are non-contact forces that can be either attractive or repulsive.  

Attractive magnetic forces pull two objects towards each other. For example, the different poles of two magnets are attracted to each other. On the other hand, like poles experiment a repulsive force that pushes them away from each other. 

An example of attraction and repulsion in terms of charge involves static electricity. Rubbing a balloon on your hair will cause the balloon to steal electrons from your hair, charging the balloon negatively and your hair positively. If the balloon gets near the hair, it will attract it. Two ballons charged in the same way obtain the same type of charge, and thus, they repel each other.

Attraction and repulsion are opposite characteristics of non-contact forces. An attractive force pulls objects together, whereas a repulsive force pushes objects away. 

When two objects have the same type of charge, they pull each other, tending to move closer. This is an attractive electrostatic force. Conversely, if they have different types of charge, they push each other away. Thus, the electrostatic force, in this case, is repulsive.

Final Attraction and Repulsion Quiz

Question

When do we say that a force is repulsive?

Show answer

Answer

A force is repulsive if the interacting objects are being pushed away from each other. 

Show question

Question

When do we say that a force is attractive?

Show answer

Answer

A force is attraction if the interacting objects are pulled towards each other.

Show question

Question

Coulombs law describes...

Show answer

Answer

The force between charged objects.

Show question

Question

After you rub a ballon on your hair, it can attract your hair and small pieces of paper. Which of the following is the correct explanations to this phenomena?

Show answer

Answer

After rubbing it, the ballon gets charged. Therefore, when the ballon is near those objects, it attracts the positive charges in their atoms. 

Show question

Question

Which of the following forces can only be attractive?

Show answer

Answer

Gravity.

Show question

Question

How is the force between a north pole of a magnet and the north pole of another magnet?

Show answer

Answer

Repulsive.

Show question

Question

How is the force between a positively charged object and a negatively charged object?

Show answer

Answer

Attractive.

Show question

Question

This scientist discovered that the force of two charged objects is directly proportional to their charges and inversely proportional to the squared of the distance between them. 

Show answer

Answer

Charles-Augustin de Coulomb.

Show question

Question

Neodymium magnets are very  strong permanent magnets. If you had one you could use it to move some breakfast cereal flakes floating on milk or water. Why does this happen?  

Show answer

Answer

Some breakfast cereals have iron which is a metal strongly attracted by magnets.

Show question

Question

A positively charged object always feels a repulsive electric force. 

Show answer

Answer

False.

Show question

Question

A compass uses a magnetic needle to work. The needle in the compass is free to move and the magnetic north pole of the needle is attracted to the geographic north pole of the earth. This is because ...

Show answer

Answer

The earth's geographic north pole is a magnetic south pole. 

Show question

Question

What is the SI unit used to measure electric charge? 

Show answer

Answer

Coulombs.

Show question

Question

Charles-Augustin de Coulomb used a torsion balanced in his experiments. With it we was able to find a mathematical expression to describe...

Show answer

Answer

Electrostatic Force.

Show question

Question

Some metals can be strongly attracted to magnets. This is because ...

Show answer

Answer

The magnetic zones in the metal align with the magnetic field of the magnet, behaving like a magnet themselves. 

Show question

Question

In which of the following objects experience a repulsive force?

Show answer

Answer

Two positively charged objects next to each other.

Show question

60%

of the users don't pass the Attraction and Repulsion quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Just Signed up?

Yes
No, I'll do it now

Sign up to highlight and take notes. It’s 100% free.